The present invention relates generally to medical imaging systems. More particularly, the present invention relates to methods and systems for thermal management in X-ray and other imaging tubes.
Imaging tubes such as X-ray tubes, CT tubes and vascular tubes often operate at high average power loads for long durations of time. For example, cardiovascular tubes used for bypass surgery may run continuously for more than forty minutes at high operating loads. This results in high thermal stresses on the various components inside the tubes.
An X-ray tube typically includes a casing and an insert with a cathode assembly and a rotating anode assembly acting as the target. The anode assembly includes a target member, which is rotated at a high speed by attaching the target to a large rotor with the rotor forming the armature of a motor. The rotor typically rotates on a highly specialized ball bearing system.
When X-ray tubes are operated at a high average power, such as five kilowatts (KW) or more, the bearings experience high thermal stresses due to the increased temperature when the bearings are continuously operated at temperatures higher than the safe temperature limit for their operation, the life of the bearings decreases exponentially, thereby resulting in early failure. This is due in part to premature decreases in the critical mechanical properties of the bearings, such as hardness and yield strength. Thus, it is important to provide adequate heat insulation to the bearings.
Existing thermal barriers in such systems may not provide sufficient heat insulation to the bearings. This is because thermal management in the imaging tubes is restricted by the operating conditions, which include a very low pressure (e.g., 10−3-10−6 torr) and very high temperatures in the order of 800 degrees Celsius (C) or more near the bearing hub inside the tube. Most thermal management materials undergo severe physical and chemical degradation in the form of oxidation under such conditions. An effective thermal management material also needs to be vacuum compatible. Other constraints also are present, such as electrical conductivity to allow high voltage to pass through the anode and cathode. The strength of the material also is a key factor that affects its use as a good insulation material. In addition, known thermal management materials have complex thermal insulator configurations that may require many design changes in existing tubes, thus increasing the cost of manufacture.
Thus, known imaging tube designs do not provide effective thermal management to the bearings and other components in the system at high operating loads. Further, these systems are not flexible enough to operate for long durations at high operating loads.